Magnesium
Explanation
Essential elements for plant growth and metabolism are classified into two categories based on the quantity required by the plant:
- Macro-nutrients: Required in large amounts (in excess of 10 mmole kg-1 of dry matter). Examples include Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulphur.
- Micro-nutrients (Trace Elements): Required in very small amounts (less than 10 mmole kg-1 of dry matter). Examples include Iron, Manganese, Copper, Molybdenum, Zinc, Boron, Chlorine, and Nickel.
Analysis of Options
- Magnesium (Mg): It is a macro-nutrient. It forms the central atom of the chlorophyll molecule and is essential for photosynthesis. It also activates enzymes involved in respiration and DNA/RNA synthesis.
- Iron (Fe): It is a micro-nutrient. Although required in larger amounts than other micronutrients, it falls under the trace element category. It is crucial for electron transfer (ferredoxin, cytochromes).
- Copper (Cu): It is a micro-nutrient involved in redox reactions and is a component of enzymes like plastocyanin.
- Chlorine (Cl): It is a micro-nutrient essential for the water-splitting reaction in photosynthesis leading to oxygen evolution.
Key Takeaway
Magnesium is a macro-nutrient essential for the structural integrity of chlorophyll, whereas Iron, Copper, and Chlorine are classified as micro-nutrients.